The present invention relates to content processing system capable of processing various digital contents such as image data and sound data, and a content protecting method.
Recently, with the advance of computer technologies, various electronic apparatuses such as multimedia personal computers, set-top boxes, players, and game machines have been developed. The electronic apparatuses of this type can reproduce diverse digital contents such as image data and sound data stored in recording media, and can also use digital contents by downloading them through, e.g., the Internet.
These digital contents can be copied or downloaded without being degraded by the use of digital encoding technologies such as MPEG2 and MP3. Hence, the necessity of technologies for protecting such digital contents from illegal use is being demanded from the viewpoint of copyright protection.
Recently, therefore, these mechanisms of authentication and encryption are beginning to be developed primarily for memory cards and removable media, which allow exchange of contents only between electronic apparatuses having a valid copyright protecting function and recording media.
A representative authentication and encryption technology is a mechanism which performs authentication by using device identification information unique to an electronic apparatus and a key matrix called revocation list information recorded on a recording medium, thereby eliminating invalid electronic apparatuses and issuing an encryption key to valid electronic apparatuses. By using this mechanism, it is possible, by simply updating only the revocation list information recorded on a recording medium before shipment, to nullify the use of device identification information found to be hacked, thereby protecting contents against illegal attacks.
As the data size of the revocation list information is increased, the number of the combinations of device identification information to be eliminated can be increased. Accordingly, the data size is preferably as large as possible.
In practice, however, different types of recording media have largely different storage capacities. Therefore, if pieces of revocation list information having a common size are used between different kinds of media, various problems arise. For example, if the size of the revocation list information is too large for a recording medium such as a memory card having a relatively small storage capacity, a memory size to be allocated as a user data area is reduced. Also, the number of device identification information which can be authenticated by the revocation list information is finite. Hence, if common revocation list information is defined between different types of media, problems such as an insufficient number of allocable device identification information arise.
On the other hand, when revocation information and corresponding device identification information are defined for each type of recording medium, it is possible to use revocation list information having a size optimum for each recording media type. When this is the case, however, an apparatus, such as a personal computer, capable of handling various types of recording media poses the following problem in regard to the compatibility between the recording media.
For example, an application program running on a valid apparatus which is assigned device identification information for a memory card can process a content on a memory card to be used, by performing authentication by using the device identification information of the apparatus and revocation list information previously recorded on the memory card. However, when a recording medium, such as a DVD-RAM, other than a memory card is to be handled, processing such as transfer of a content from the memory card to the DVD-RAM cannot be performed because revocation list information previously recorded on the DVD-RAM cannot be processed by the device identification information for a memory card. Accordingly, even when a user has purchased a valid DVD-RAM drive corresponding to a copyright protecting function, DVD-RAMs cannot be actually handled similarly to memory cards. This is very inconvenient for the user.